1. Field of the Invention
The invention relates to an aqueous dispersion for the chemical mechanical polishing of an oxidic surface and a process for its production.
2. Discussion of the Background
Aqueous dispersions containing silicon dioxide are used in a broad range of applications. Examples of applications include the coating of paper, the production of glass fibers and quartz glass, and the chemical mechanical polishing of semiconductor substrates (CMP process).
Conventional dispersions mostly originate from colloidal silicon dioxide, silica sols, or from pyrogenically produced silicon dioxide.
Dispersions containing colloidal silicon dioxide generally have a defined, small particle size and a good dispersion stability. In chemical mechanical polishing, the defect rate, for example the number of scratches, on the polished surface is low. The disadvantage, however, is the low removal rate in the polishing of oxidic surfaces in comparison to dispersions containing pyrogenically produced silicon dioxide.
On the other hand, dispersions containing pyrogenically produced silicon dioxide cause a larger number of scratches due to the aggregation and agglomeration of primary particles, giving rise to hard particles. Dispersing the aggregates and agglomerates proves to be difficult, the dispersions are less stable and have a tendency to sediment or to gel.
EP-A-1148026 describes a dispersion of silicon dioxide doped with aluminum oxide by means of an aerosol and the use of this dispersion to manufacture coating slips in the ink-jet sector and for chemical mechanical polishing. An aqueous dispersion having a very broad range of aluminum oxide doping from 1 to 200,000 ppm is claimed. It has been found, however, that although a dispersion defined in this way can advantageously be used in the ink-jet sector, it does not display a satisfactory polishing performance in chemical mechanical polishing. Thus a dispersion produced according to EP-A-1148026 and containing a silicon dioxide powder doped with 20 wt. % aluminum oxide displays a very high defect rate, while a low-doped powder, containing for example 10 ppm aluminum oxide, displays a low removal rate.